Engine failure leads to forced landing of Sling 2 near N1 freeway

Casualties unknown • Private farm approximately 500m Westerly of N1 freeway Pretoria, ZA

An engine failure caused by excessive RPM led to a forced landing of a Sling 2 aircraft in South Africa, resulting in no injuries but significant aircraft damage.

What happened

On 02 December 2015, a Sling 2 aircraft, registration ZU-WMM, departed from Wonderboom Aerodrome (FAWB) for a private flight. Shortly after takeoff, while cruising at approximately 5,800 feet AGL, the pilot observed a red warning light on the engine's fuel-injected Rotax system. Within seconds of this indication, the engine failed completely.

Following an unsuccessful attempt to restart the engine, the pilot initiated an emergency forced landing near a private airstrip by the N1 freeway. During the descent, the aircraft struck a boundary fence with its left wing before impacting the ground. The aircraft then skidded approximately 70 metres on its belly. Despite the impact, there were no injuries to the two occupants on board.

The investigation

SACAA AIID investigators examined the wreckage and maintenance records of the Sling 2. The investigation focused on the mechanical state of the Rotax 912 engine and the pilot's awareness of engine parameters. Maintenance records indicated the aircraft had undergone its annual inspection only weeks prior and was otherwise properly maintained.

Technical analysis of the engine revealed that the failure was linked to thermal issues. The investigation established that the engine had been running at much higher revolutions than permitted for an extended period. While the pilot noted the warning light, the investigation found the pilot was not aware of the specific over-rev condition occurring on the Electronic Flight Instrument System (EFIS) screen.

Findings

  • The engine failure was caused by operating the engine at 6100 to 6500 RPM for a duration of 11 minutes and 29 seconds.
  • This exceeded the manufacturer's limit, which restricts operation to a maximum of 5800 RPM for no more than 5 minutes.
  • The excessive revolutions led to high temperatures and the subsequent failure of internal mechanical engine components.
  • The pilot, who had recently completed conversion training from analogue instruments to EFIS, appeared unaware of the over-rev warning on the digital display.
  • Weather conditions were clear with good visibility, and therefore played no role in the accident.

Safety action

Following the investigation, it was recommended that the Director of Civil Aviation review training protocols regarding the conversion from analogue instruments to EFIS. The recommendation emphasizes the need for a robust syllabus and sufficient training time to ensure pilots are fully competent in monitoring digital engine parameters after such a transition.

Probable cause

The engine failure resulted from operating the engine at excessive RPM (6100-6500) for over 11 minutes, causing overheating and mechanical failure, followed by an unsuccessful forced landing.

Frequently asked questions

What happened in the 2015-12-02 Sling 2 accident near Private farm approximately 500m Westerly of N1 freeway Pretoria, ZA?

An engine failure caused by excessive RPM led to a forced landing of a Sling 2 aircraft in South Africa, resulting in no injuries but significant aircraft damage.

What aircraft was involved and where did it happen?

The accident on 2015-12-02 involved a Sling 2, registration ZU-WMM, at Private farm approximately 500m Westerly of N1 freeway Pretoria, ZA.

What was the probable cause of the accident?

The engine failure resulted from operating the engine at excessive RPM (6100-6500) for over 11 minutes, causing overheating and mechanical failure, followed by an unsuccessful forced landing.

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